Flexible polyurethane foams are foams having an open cell structure, an extremely low compression hardness and flexibility. Among them, a thick-plate type foam having a large width or a long continuous foam block is called a “slab stock” or, as abbreviated, a “slab” which is subsequently used as cut into a proper shape. Especially, a polyester type flexible polyurethane foam is light in weight and excellent in resiliency, and therefore it is widely used for products such as automobiles, household furniture, bedding, cushions or clothing.
A polyurethane foam is produced by reacting a polyisocyanate and a polyol in the presence of a catalyst and, if necessary, a blowing agent or a surfactant, and further if necessary, other additives such as cross linking agents. In the production of a polyester type flexible polyurethane foam, usually, a polyester polyol is used as the polyol, and an amine type catalyst or a combination of the amine type catalyst and a tin type catalyst is used as the catalyst, so as to produce a good foam.
In order to produce a polyester type flexible polyurethane foam having good foam formability (shrinkage and deformation) without occurrence of scorching in the foam, a specific amine compound is used as the catalyst. For example, N-methylmorpholine, N-ethylmorpholine or 1,4-dimethylpiperazine is known.
However, in a case where the above amine compound is used as the catalyst for a polyester type flexible polyurethane foam, the amine compound remains in a free-form in a made foam and is gradually discharged as a volatile amine, and therefore a product tends to have odor problems.
As a method for solving such a problem, proposed is a method for producing a polyurethane foam by using e.g. N-methylimidazole or 1,2-dimethylimidazole as a low amine odor catalyst, instead of the above amine compounds (see e.g. Patent Document 1.)
Further, proposed is a method of using an amine compound having primary and secondary amino groups or a hydroxyalkyl group, reactive with a polyisocyanate, in its molecule, for producing the polyurethane foam (for example, see Patent Documents 2 to 5.)
According to the above Patent Documents, such amine compounds are fixed in the polyurethane resin structure, in such a form as reacted with the polyisocyanate, whereby it is possible to avoid the above problem.
However, if such amine compounds having the reactive groups in their molecules are used for producing a polyester type flexible polyurethane foam, there was a problem that a good foam cannot be made due to shrinkage of the foam or occurrence of scorching in the interior of the foam.
On the other hand, it has been known that in a method for producing a polyether type flexible polyurethane foam by using a polyether polyol as the polyol, a tin catalyst (such as stannous octoate) and a tertiary amine catalyst (such as hydroxyethyl morpholine or dimethyl isopropanol amine) are used in combination as catalysts (see Patent Document 6). However, it has been unknown to use the hydroxyethyl morpholine or dimethyl isopropanol amine as a catalyst for a polyether type flexible polyurethane foam, without the combined use with a tin catalyst.
Patent Document 1: JP-A-7-258367
Patent Document 2: JP-A-46-4846
Patent Document 3: JP-A-4-85317
Patent Document 4: JP-A-2003-206327
Patent Document 5: JP-A-2004-27010
Patent Document 6: U.K. Patent No. 1,091,604